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content/en/docs/tasks/inject-data-application/define-command-argument-container.md

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+---
+title: Define a Command and Arguments for a Container
+content_template: templates/task
+---
+
+{{% capture overview %}}
+
+This page shows how to define commands and arguments when you run a container
+in a {{< glossary_tooltip term_id="pod" >}}.
+
+{{% /capture %}}
+
+
+{{% capture prerequisites %}}
+
+{{< include "task-tutorial-prereqs.md" >}} {{< version-check >}}
+
+{{% /capture %}}
+
+
+{{% capture steps %}}
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+## Define a command and arguments when you create a Pod
+
+When you create a Pod, you can define a command and arguments for the
+containers that run in the Pod. To define a command, include the `command`
+field in the configuration file. To define arguments for the command, include
+the `args` field in the configuration file. The command and arguments that
+you define cannot be changed after the Pod is created.
+
+The command and arguments that you define in the configuration file
+override the default command and arguments provided by the container image.
+If you define args, but do not define a command, the default command is used
+with your new arguments.
+
+In this exercise, you create a Pod that runs one container. The configuration
+file for the Pod defines a command and two arguments:
+
+{{< code file="commands.yaml" >}}
+
+1. Create a Pod based on the YAML configuration file:
+
+       kubectl create -f https://k8s.io/docs/tasks/inject-data-application/commands.yaml
+
+1. List the running Pods:
+
+       kubectl get pods
+
+    The output shows that the container that ran in the command-demo Pod has
+    completed.
+
+1. To see the output of the command that ran in the container, view the logs
+from the Pod:
+
+       kubectl logs command-demo
+
+    The output shows the values of the HOSTNAME and KUBERNETES_PORT environment
+    variables:
+
+        command-demo
+        tcp://10.3.240.1:443
+
+## Use environment variables to define arguments
+
+In the preceding example, you defined the arguments directly by
+providing strings. As an alternative to providing strings directly,
+you can define arguments by using environment variables:
+
+    env:
+    - name: MESSAGE
+      value: "hello world"
+    command: ["/bin/echo"]
+    args: ["$(MESSAGE)"]
+
+This means you can define an argument for a Pod using any of
+the techniques available for defining environment variables, including
+[ConfigMaps](/docs/tasks/configure-pod-container/configure-pod-configmap/)
+and
+[Secrets](/docs/concepts/configuration/secret/).
+
+{{< note >}}
+**Note:** The environment variable appears in parentheses, `"$(VAR)"`. This is
+required for the variable to be expanded in the `command` or `args` field.
+{{< /note >}}
+
+## Run a command in a shell
+
+In some cases, you need your command to run in a shell. For example, your
+command might consist of several commands piped together, or it might be a shell
+script. To run your command in a shell, wrap it like this:
+
+    command: ["/bin/sh"]
+    args: ["-c", "while true; do echo hello; sleep 10;done"]
+
+## Notes
+
+This table summarizes the field names used by Docker and Kubernetes.
+
+|              Description               |    Docker field name   | Kubernetes field name |
+|----------------------------------------|------------------------|-----------------------|
+|  The command run by the container      |   Entrypoint           |      command          |
+|  The arguments passed to the command   |   Cmd                  |      args             |
+
+When you override the default Entrypoint and Cmd, these rules apply:
+
+* If you do not supply `command` or `args` for a Container, the defaults defined
+in the Docker image are used.
+
+* If you supply a `command` but no `args` for a Container, only the supplied
+`command` is used. The default EntryPoint and the default Cmd defined in the Docker
+image are ignored.
+
+* If you supply only `args` for a Container, the default Entrypoint defined in
+the Docker image is run with the `args` that you supplied.
+
+* If you supply a `command` and `args`, the default Entrypoint and the default
+Cmd defined in the Docker image are ignored. Your `command` is run with your
+`args`.
+
+Here are some examples:
+
+| Image Entrypoint   |    Image Cmd     | Container command   |  Container args    |    Command run   |
+|--------------------|------------------|---------------------|--------------------|------------------|
+|     `[/ep-1]`      |   `[foo bar]`    |   &lt;not set&gt;   |   &lt;not set&gt;  | `[ep-1 foo bar]` |
+|     `[/ep-1]`      |   `[foo bar]`    |      `[/ep-2]`      |   &lt;not set&gt;  |     `[ep-2]`     |
+|     `[/ep-1]`      |   `[foo bar]`    |   &lt;not set&gt;   |     `[zoo boo]`    | `[ep-1 zoo boo]` |
+|     `[/ep-1]`      |   `[foo bar]`    |   `[/ep-2]`         |     `[zoo boo]`    | `[ep-2 zoo boo]` |
+
+
+{{% /capture %}}
+
+{{% capture whatsnext %}}
+
+* Learn more about [containers and commands](/docs/user-guide/containers/).
+* Learn more about [configuring pods and containers](/docs/tasks/).
+* Learn more about [running commands in a container](/docs/tasks/debug-application-cluster/get-shell-running-container/).
+* See [Container](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#container-v1-core).
+
+{{% /capture %}}
+
+
+